For a professional television camera, a normal chain of processing the video signal from scene-image to a display unit consists of the elements: optical lens unit, electronic pick-up elements, a video processing circuit coupled to the pick-up elements and a display unit. The lens unit projects the scene to be broadcasted horizontally and vertically in reversed order on the pick-up elements. The pick-up elements are readout sequentially in such a way that the horizontal and vertical position of the picture is reversed again to retain the normal picture. The video processing circuit generates from the raw data stream a signal useable for the display unit and provides in particular an output signal in accordance with a required video standard.
When a television camera is used with a lens unit, which is originally designed for film applications, a problem occurs. A film lens unit projects the scene in a non-reversed way on the pick-up element, in this case generally light sensitive film material. If such a lens unit is used with a television broadcast camera, the output signal of the respective pick-up elements has to be reversed horizontally and vertically.
A straightforward way to reverse an electronic picture is to use two electronic memories in which two complete pictures can be stored. For a continued picture reversal, a first picture is stored in the first memory. The second picture is stored in the second memory and simultaneously the first memory is readout in reversed order and sent to the output. When the second picture is stored in the second memory, then the first memory is available for the third picture. The third picture is then stored in the first memory, and at the same time the second memory is readout in reversed order, and so on for the subsequent pictures. This results in a continuous picture reversal for a video signal. Because professional cameras provide a video signal with a high resolution, a considerably large memory is required for a method of this kind.
Horizontal scan reversal methods and respective circuits are known for example from KR 9507034, JP 02260877, CA 2127608, JP 2158436 and JP 63019995.